The molecular mechanisms involved in DNA replication are being studied. Proteins involved in both phage lambda and E. coli replication are being purified and haracterized in vitro. The present emphasis is to gain insight into the process of initiation of chromosome replication. The replication of double-stranded circular lambda dv DNA is being studied in crude extracts of uninfected E. coli supplemented with the two phage proteins necessary for replication. The biochemistry of lambda site-specific recombination is also being studied. The proteins required for excisive recombination have been purified and are being characterized. The roles of the various proteins in recombination is being pursued.